Heterogeneity among AIDS retroviral genomes is a distinct feature of lentiviruses, Molecular cloning, restriction enzyme analysis, nucleotide sequencing, and polymerase chain reaction techniques were used to characterize isolates of Human Immunodeficiency Virus Type 1 (HIV-1). The objective was to obtain information pertaining to the structure and diversity of HIV with respect to its biochemical, pathogenic, and antigenic variability. Most HIV isolates we have cloned are T-cell tropic. We have succeeded in obtaining a complete molecular clone from a macrophagetropic viral isolate. Although T-cells are the major target for HIV replication in peripheral blood, macrophages represent the predominant HIV-infected cell type in most tissues. Macrophages are probably the primary reservoir of HIV, and sustain a persistent infection in individuals for many years. A single HIV macrophagetropic isolate was molecularly cloned, and upon transfection into HeLa cells followed by cocultivation on PBLs or macrophages, produced viral particles (RT). The virus produced was infectious and could replicate in either PBLs or macrophages. It was unable to replicate in a continuous T-cell line (CEM). Growth studies and biochemical analysis with this isolate are in progress.